Circuit arrangement and method for igniting a high-pressure discharge lamp

ABSTRACT

A circuit arrangement for a high-pressure discharge lamp, having a main combustion chamber with first and second main electrodes and an auxiliary combustion chamber including: an inverter having first and second electronic switches and first and second output terminals; a drive circuit for the electronic switches; and an auxiliary starting circuit. The auxiliary starting circuit has input terminals coupled to the output terminals of the inverter; a first output terminal for the first main electrode; a second output terminal for the second main electrode; and an auxiliary electrode arranged on the side of the first output terminal for inducing an auxiliary starting voltage in the auxiliary combustion chamber. The auxiliary starting circuit includes a cascade circuit formed by the auxiliary electrode and the second output terminal of the auxiliary starting circuit, which provides a voltage for starting the high-pressure discharge lamp.

RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/EP2006/068973 filedNov. 28, 2006.

FIELD OF THE INVENTION

The present invention relates to a circuit arrangement for starting ahigh-pressure discharge lamp, which has a main combustion chamber with afirst and a second main electrode and an auxiliary combustion chamber,with an inverter, which has at least one first and one second electronicswitch and one first and one second output terminal, a drive circuit fordriving the electronic switches of the inverter, an auxiliary startingcircuit, which has a first and a second input terminal, the first inputterminal being coupled to the first output terminal of the inverter, andthe second input terminal being coupled to the second output terminal ofthe inverter, a first output terminal for connecting the first mainelectrode of the high-pressure discharge lamp, a second output terminalfor connecting the second main electrode of the high-pressure dischargelamp and an auxiliary electrode for inducing an auxiliary startingvoltage in the auxiliary combustion chamber, the auxiliary electrodebeing arranged on the side of the first output terminal. The inventionmoreover relates to a method for starting a high-pressure dischargelamp, which has a main combustion chamber with a first and a second mainelectrode and an auxiliary combustion chamber, using such a circuitarrangement.

BACKGROUND OF THE INVENTION

Such generic circuit arrangements are used, for example, for rearprojections in the TV sector. In this case, the high-pressure dischargelamp is operated with a constant square-wave current or else steppedsquare-wave currents. A typical operating frequency is 100 Hz. In orderto start the high-pressure discharge lamp, at present two differentvariants are used: the first variant is resonance starting, which can berealized with comparatively little complexity but which has thesignificant disadvantage of a long restarting time of the hothigh-pressure discharge lamp of approximately 120 s. In the case ofresonance starting, an LC circuit, for example, is brought to resonanceand the high voltage resulting from resonance magnification is used forstarting purposes. The second known variant is so-called pulse starting,which is characterized by the fact that a component, for example a sidacor a spark discharge gap, is used for the breakdown. This method has arelatively short restarting time of from 10 s to 20 s. Unfortunately,circuit arrangements with pulse starting are characterized by markedlyincreased implementation complexity, which results in undesirably highcosts.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a circuit arrangementand a method that enable the restarting of the still hot high-pressuredischarge lamp with as short a restarting time as possible and withoperating costs which are as low as possible.

The present invention is based on the knowledge that the above objectcan be achieved if a resonance starting system is used as a basis whichis supplemented by an auxiliary starting circuit, which is designed togenerate a polarizing high voltage, which is applied in correct phasesequence for achieving a maximum voltage between the auxiliary electrodeand the opposite main electrode of the high-pressure discharge lamp. Forthis purpose, the auxiliary starting circuit comprises a cascadecircuit, which provides a voltage for starting the high-pressuredischarge lamp at the output of said circuit, the output of the cascadecircuit being formed by the auxiliary electrode and the second outputterminal of the auxiliary starting circuit.

This measure means that the auxiliary starting circuit only needs to bedesigned for very low currents, which ultimately results in a veryreliable starting system in combination with short restarting timesalongside low costs.

In a preferred embodiment, the starting circuit furthermore comprises aresonant capacitor, which is coupled between the first and the secondinput terminal of the auxiliary starting circuit, the first terminal ofthe resonant capacitor being coupled to the first output terminal of theauxiliary starting circuit, and the second terminal of the resonantcapacitor being coupled to the second output terminal of the auxiliarystarting circuit.

Preferably, the auxiliary starting circuit furthermore comprises a firstcascade capacitor, a first cascade diode, and a second cascade diode,the first terminal of the resonant capacitor furthermore being coupledto the auxiliary electrode via the series circuit comprising the firstcascade capacitor and the second cascade diode, the node of the firstcascade capacitor being coupled to the anode of the second cascade diodeand to the cathode of the first cascade diode, and the anode of thefirst cascade diode being coupled to the second terminal of the resonantcapacitor. This provides a starting cascade which generates a highvoltage in a targeted manner and applies it to the auxiliary electrode.As a result, an excimer discharge is generated in the auxiliarycombustion chamber, which excimer discharge triggers the ignitionprocess in the main combustion chamber.

Given suitable dimensions, the voltage applied to the resonant capacitorcan be approximately tripled. Starting from a voltage across theresonant capacitor of approximately 2.5 kV, it is therefore possible togenerate a starting voltage of up to 7.5 kV by using the procedureaccording to an embodiment of the invention. This auxiliary voltage ispresent between the auxiliary electrode and the opposite main electrode.

Preferably, the auxiliary starting circuit furthermore comprises anonreactive resistor, which is coupled between the second terminal ofthe resonant capacitor and the anode of the first cascade diode. As aresult, the rate at which the first cascade capacitor is charged can becontrolled, as well as the residual voltage which remains during regularoperation of the high-pressure discharge lamp. In this case, theresistance of the nonreactive resistor can also approach zero, however.

Preferably, the auxiliary starting circuit furthermore comprises asecond cascade capacitor, whose first terminal is coupled to the anodeof the first cascade diode, and whose second terminal is coupled to theauxiliary electrode. As a result, the system-related capacitance betweenthe auxiliary electrode and the opposite main electrode can beincreased. This reduces the ripple of the voltage and shortens therestarting time.

In a preferred embodiment, the auxiliary starting circuit furthermorecomprises a matching network, which is coupled between the first and thesecond input terminal of the auxiliary starting circuit and the firstand the second terminal of the resonant capacitor. Preferably, thematching network in this case comprises at least one inductance, inparticular a first and a second inductance, the first inductance beingcoupled in series between the first input terminal of the auxiliarystarting circuit and the first terminal of the resonant capacitor, andthe second inductance being coupled in series between the second inputterminal of the auxiliary starting circuit and the second terminal ofthe resonant capacitor. The at least one inductance forms, together withthe resonant capacitor, the resonant circuit, which is the basis for thepresent auxiliary starting circuit. As a result, the fixed outputvoltage pattern of the inverter can moreover be converted in a simpleway with very low losses into the current which is required by thehigh-pressure discharge lamp during operation. At the same time, thehigh-pressure discharge lamp is provided with the required freedom forsetting its dedicated voltage, which is produced given the currentprovided at that time. Moreover, the at least one inductance acts as areturn filter, which damps the disruptive influences of thehigh-pressure discharge lamp on the inverter and which at the same timepositively influences the switchover operations of the inverter itself.

If the first cascade capacitor, the first cascade diode and the secondcascade diode form a first cascade stage, it can furthermore preferablybe provided that the auxiliary starting circuit comprises at least onesecond cascade stage, which is coupled between the first cascade stageand the first output terminal, the second output terminal and theauxiliary electrode of the starting circuit. Arranging a plurality ofcascade stages in series makes it possible to set the voltage providedat the output of the auxiliary starting circuit to be as high asdesired.

The preferred embodiments mentioned with reference to the circuitarrangement according to the invention and the advantages thereof apply,if appropriate, correspondingly to the method according to theinvention.

BRIEF DESCRIPTION OF THE DRAWING(S)

Exemplary embodiments of a circuit arrangement according to theinvention will now be described in more detail below with reference tothe attached drawings, in which:

FIG. 1 shows a schematic illustration of the design of a circuitarrangement according to the invention;

FIG. 2 shows the time profile of three variables from FIG. 1, with thesecond cascade diode being replaced by a short circuit; and

FIG. 3 shows the time profile of the variables from FIG. 2 with thesecond cascade diode inserted.

PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 shows a schematic illustration of the design of an exemplaryembodiment of a circuit arrangement according to the invention. It showsan inverter 10, with a DC voltage, generally the so-called intermediatecircuit voltage U_(ZW), present at the input terminals WE1, WE2 of saidinverter. These switches S1 to S4 of the inverter 10 are driven in aknown manner by a control apparatus 12 in order to generate asquare-wave signal between the output terminals WA1, WA2 of the inverter10. In a preferred exemplary embodiment, the sequence of the square-wavesignal is between 30 kHz and 100 kHz. As is obvious to a person skilledin the art, the inverter 10 can also be implemented as a half-bridgecircuit, instead of as a full-bridge circuit.

The output terminal WA1 of the inverter 10 is connected to an inputterminal ZE1, and the output terminal WA2 of the inverter 10 isconnected to an input terminal ZE2 of an auxiliary starting circuit 14.The auxiliary starting circuit 14 first has a matching network, whichcomprises the inductances L1 and L2. These form, together with aresonant capacitor C_(RES), a resonant circuit. In this case, theinductances L1 and L2 may be two independent components; they can havethe same value, but do not have to, wherein it is possible in particularfor one of the two inductances to approach zero. They can particularlypreferably also be implemented by a combined component, in which twowindings are applied to one and the same magnetic core. In this case,the node between the inductance L1 and the resonant capacitor C_(res) isdenoted by the node 2, and the node between the inductance L2 and theresonant capacitor C_(res) is denoted as the node 1. The node 2 forms afirst output terminal ZA1 of the auxiliary starting circuit 14, and thenode 1 forms an output ZA2 of the auxiliary starting circuit 14. Theauxiliary starting circuit 14 moreover has an auxiliary electrode HiE,which is arranged over an auxiliary combustion chamber of thehigh-pressure discharge lamp LA and has a helical formation. The outputterminal ZA1 of the auxiliary starting circuit 14 is connected to afirst main electrode HaE1, and the output terminal ZA2 is connected to asecond main electrode HaE2 of the high-pressure discharge lamp LA, withthe result that the first and the second main electrode HaE1, HaE2 areintroduced into the main combustion chamber HaBk thereof. The seriescircuit comprising a first cascade capacitor C_(HV1) and a secondcascade diode D2 is arranged between the node 2 and the auxiliaryelectrode HiE, with the cathode of the cascade diode D2 being denoted asthe node 3, and the node between the first cascade capacitor C_(HV1) andthe second cascade diode D2 being denoted as the node 5. The seriescircuit comprising a nonreactive resistor R and a first cascade diode D1is arranged between the node 1 and the node 5, the node between thenonreactive resistor R and the anode of the cascade diode D1 beingdenoted as the node 4. Optionally, a second cascade capacitor C_(sys)can be arranged between the node 4 and the node 3. As is indicated inFIG. 1, the voltage drop across the resonant capacitor C_(res), i.e. thevoltage drop between the nodes 1 and 2, is denoted as the voltage U₁₂.The voltage drop between the node 1 and the cathode of the secondcascade diode D2, i.e. between the nodes 1 and 3, is denoted as thevoltage U₁₃. If the voltage between the nodes 3 and 2 is denoted as U₃₂,the voltage U₁₃ therefore results in accordance with the followingequation:U ₁₃ =U ₁₂ −U ₃₂.

The determination of the voltage U₁₃ in this way is necessary since thevoltage U₁₃ is very highly resistive and therefore is difficult tomeasure, in contrast to the voltages U₁₂ and U₃₂.

In order to describe the way in which the circuit functions, referenceis furthermore made to FIGS. 2 and 3, where FIG. 2 shows the timeprofile of the voltages U₁₂, U₃₂ and U₁₃ if the second cascade diode D2is replaced by a short circuit and FIG. 3 shows the correspondingprofile with the second cascade diode D2 inserted. It should furthermorebe noted that the common zero line for the voltages U₁₂, U₃₂ and U₁₃ isthe correspondingly identified central line in the graph illustrated inFIGS. 2 and 3.

The voltage U₁₂ is produced across the resonant capacitor C_(res) viathe series resonant circuit, which comprises the inductances L1 and L2and the resonant capacitor C_(res). In this regard, the following shouldbe noted: by operating the full-bridge circuit at a third, a fifth or aseventh of the resonant frequency, which is defined by the componentsL1, L2 and C_(res), the full-bridge circuit is switched over preciselyat the zero crossing of the resonant voltage formed. These switchovertimes are shown in FIGS. 2 and 3 by virtue of the fact that theresultant resonant voltages assume a positive or negative maximum. Inbetween these times, no energy is supplied to the resonant circuit andthe voltages decay in accordance with an exponential function. As aresult of this stimulation by means of a square-wave voltage, theresonant voltage across the resonant capacitor C_(res) is formed as asinusoidal voltage.

The voltage U₁₂ is a sinusoidal AC voltage without a DC component. Bymeans of this voltage, the first cascade capacitor C_(HV1) is chargedvia the nonreactive resistor R, which acts as the charging resistor, andthe first cascade diode D1 if the node 1 has a positive polarity inrelation to the node 2. Without the presence of the diode D2, i.e. thenodes 5 and 3 are connected by a short circuit, the first cascadecapacitor C_(HV1) has a substantially constant charge, i.e. the voltageU₃₂ is a DC voltage whose amplitude virtually does not change; see inthis regard the illustration in FIG. 2. The voltage U₁₃ results by thedifference being formed between the voltage U₁₂ and the voltage U₃₂. InFIG. 2, the voltage U₁₃ is therefore lower than the voltage U₁₂ by theabsolute value of U₃₂. This voltage is present between the second mainelectrode HaE2 and the auxiliary electrode HiE and assists the startingby generation of an excimer discharge in the auxiliary combustionchamber HiBk.

As is demonstrated by a comparison of the time profile of the voltageU₃₂ in FIG. 3 and of the voltage U₃₂ in FIG. 2, inserting a secondcascade diode D2 makes it possible to achieve a situation in which thevoltage U₃₂ likewise has a sinusoidal profile, with the smallestamplitude corresponding to the voltage U₃₂ in FIG. 2. This means thatthe time profile of the voltage U₁₃ now no longer falls to zero, butforms a markedly leading mean value. As a result, the production of anexcimer discharge in the auxiliary combustion chamber is favoredconsiderably, as a result of which it is possible for the restartingtime to be shortened in comparison with circuit arrangements without anauxiliary starting circuit according to the invention by up to 50%.

In relation to the difference between FIGS. 2 and 3: first in relationto FIG. 2, i.e. the variant without the second cascade diode: if apositive half cycle is present across the first cascade diode D1, thefirst cascade capacitor C_(HV1) is thereby charged. If a negative halfcycle is present across the first cascade diode D1, the second cascadecapacitor C_(sys) is thereby charged. Without the second cascade diodeD2, however, the capacitor C_(sys) is discharged again on the nextpositive half cycle across the first cascade diode D1. As a result, U₁₂becomes equal to U₃₂, as a result of which the voltage U₁₃ has zeropoints. A second cascade diode D2 prevents the discharge of the secondcascade capacitor C. This prevents U₁₂ from becoming equal to U₃₂, as aresult of which U₁₃ now no longer has any zero points.

Instead of providing a discrete second capacitor C_(sys), said capacitorcan also be dispensed with since this capacitance is in any caseprovided in a system-dependent manner between the auxiliary electrodeHiE and the main electrodes HaE1, HaE2.

Once the lamp LA has been restarted, the resonant circuit is suddenlyheavily damped. This circumstance is identified by the controller 12 ofthe inverter 10, whereupon the high-pressure discharge lamp is nowoperated with its continuous operation parameters.

The fact that a considerable improvement over simple resonance startingalready results with the implementation without the second cascade diodeD2, is demonstrated by a comparison of the voltages U₁₂ and U₁₃ in FIGS.2 and 3.

1. A circuit arrangement for starting a high-pressure discharge lamphaving a main combustion chamber with a first and a second mainelectrode and an auxiliary combustion chamber, comprising: an inverter,which has at least one first and one second electronic switch and onefirst and one second output terminal; a drive circuit for driving theelectronic switches of the inverter; and an auxiliary starting circuitcomprising: a first and a second input terminal, the first inputterminal being coupled to the first output terminal of the inverter, andthe second input terminal being coupled to the second output terminal ofthe inverter; a first output terminal for connecting the first mainelectrode of the high-pressure discharge lamp; a second output terminalfor connecting the second main electrode of the high-pressure dischargelamp; an auxiliary electrode for inducing an auxiliary starting voltagein the auxiliary combustion chamber, the auxiliary electrode beingarranged on the side of the first output terminal; a cascade circuit,which provides a voltage for starting the high-pressure discharge lampat the output of said circuit, the output of the cascade circuit beingformed by the auxiliary electrode and the second output terminal of theauxiliary starting circuit; a resonant capacitor, which is coupledbetween the first and the second input terminal of the auxiliarystarting circuit, a first terminal of the resonant capacitor beingcoupled to the first output terminal of the auxiliary starting circuit,and a second terminal of the resonant capacitor being coupled to thesecond output terminal of the auxiliary starting circuit; a firstcascade capacitor; a first cascade diode; and a second cascade diode,the first terminal of the resonant capacitor being coupled to theauxiliary electrode via a series circuit comprising the first cascadecapacitor and the second cascade diode; a node of the first cascadecapacitor being coupled to an anode of the second cascade diode and to acathode of the first cascade diode; and an anode of the first cascadediode being coupled to the second terminal of the resonant capacitor. 2.The circuit arrangement as claimed in claim 1, wherein the auxiliarystarting circuit further comprises a nonreactive resistor, which iscoupled between the second terminal of the resonant capacitor and theanode of the first cascade diode.
 3. The circuit arrangement as claimedin claim 1, wherein the auxiliary starting circuit further comprises asecond cascade capacitor with a first terminal that is coupled to theanode of the first cascade diode and with a second terminal that iscoupled to the auxiliary electrode.
 4. A circuit arrangement forstarting a high-pressure discharge lamp having a main combustion chamberwith a first and a second main electrode and an auxiliary combustionchamber, comprising: an inverter, which has at least one first and onesecond electronic switch and one first and one second output terminal; adrive circuit for driving the electronic switches of the inverter; andan auxiliary starting circuit comprising: a first and a second inputterminal, the first input terminal being coupled to the first outputterminal of the inverter, and the second input terminal being coupled tothe second output terminal of the inverter; a first output terminal forconnecting the first main electrode of the high-pressure discharge lamp;a second output terminal for connecting the second main electrode of thehigh-pressure discharge lamp; an auxiliary electrode for inducing anauxiliary starting voltage in the auxiliary combustion chamber, theauxiliary electrode being arranged on the side of the first outputterminal; a cascade circuit, which provides a voltage for starting thehigh-pressure discharge lamp at the output of said circuit, the outputof the cascade circuit being formed by the auxiliary electrode and thesecond output terminal of the auxiliary starting circuit; and a matchingnetwork, which is coupled between the first and the second inputterminal of the auxiliary starting circuit and the first and the secondterminal of the resonant capacitor, wherein the matching networkcomprises a first and a second inductance, the first inductance beingcoupled in series between the first input terminal of the auxiliarystarting circuit and the first terminal of the resonant capacitor, andthe second inductance being coupled in series between the second inputterminal of the auxiliary starting circuit and the second terminal ofthe resonant capacitor.
 5. The circuit arrangement as claimed in claim1, wherein at least the first cascade capacitor, the first cascade diodeand the second cascade diode form a first cascade stage, the auxiliarystarting circuit comprising at least one second cascade stage, which iscoupled between the first cascade stage and the first output terminal,the second output terminal and the auxiliary electrode of the auxiliarystarting circuit.
 6. A method for starting a high-pressure dischargelamp, which has a main combustion chamber with a first and a second mainelectrode and an auxiliary combustion chamber, using a circuitarrangement with an inverter, which has at least one first and onesecond electronic switch and one first and one second output terminal, adrive circuit for driving the electronic switches of the inverter, anauxiliary starting circuit comprising a first and a second inputterminal, the first input terminal being coupled to the first outputterminal of the inverter, and the second input terminal being coupled tothe second output terminal of the inverter, a first output terminal forconnecting the first main electrode of the high-pressure discharge lamp,a second output terminal for connecting the second main electrode of thehigh-pressure discharge lamp, and an auxiliary electrode for inducing anauxiliary starting voltage in the auxiliary combustion chamber, theauxiliary electrode being arranged on the side of the first outputterminal; an auxiliary electrode for inducing an auxiliary startingvoltage in the auxiliary combustion chamber, the auxiliary electrodebeing arranged on the side of the first output terminal; a cascadecircuit, which provides a voltage for starting the high-pressuredischarge lamp at the output of said circuit, the output of the cascadecircuit being formed by the auxiliary electrode and the second outputterminal of the auxiliary starting circuit; a resonant capacitor, whichis coupled between the first and the second input terminal of theauxiliary starting circuit, a first terminal of the resonant capacitorbeing coupled to the first output terminal of the auxiliary startingcircuit, and a second terminal of the resonant capacitor being coupledto the second output terminal of the auxiliary starting circuit; a firstcascade capacitor; a first cascade diode; and a second cascade diode,the first terminal of the resonant capacitor being coupled to theauxiliary electrode via a series circuit comprising the first cascadecapacitor and the second cascade diode; a node of the first cascadecapacitor being coupled to an anode of the second cascade diode and to acathode of the first cascade diode; and an anode of the first cascadediode being coupled to the second terminal of the resonant capacitor,wherein the method comprises: a) generating a voltage for starting thehigh-pressure discharge lamp by a cascade circuit, which is comprised bythe auxiliary starting circuit; and b) providing the voltage forstarting the high-pressure discharge lamp between the auxiliaryelectrode and the second output terminal of the auxiliary startingcircuit.
 7. A method for starting a high-pressure discharge lamp, whichhas a main combustion chamber with a first and a second main electrodeand an auxiliary combustion chamber, using a circuit arrangement with aninverter, which has at least one first and one second electronic switchand one first and one second output terminal; a drive circuit fordriving the electronic switches of the inverter; and an auxiliarystarting circuit comprising: a first and a second input terminal, thefirst input terminal being coupled to the first output terminal of theinverter, and the second input terminal being coupled to the secondoutput terminal of the inverter; a first output terminal for connectingthe first main electrode of the high-pressure discharge lamp; a secondoutput terminal for connecting the second main electrode of thehigh-pressure discharge lamp; an auxiliary electrode for inducing anauxiliary starting voltage in the auxiliary combustion chamber, theauxiliary electrode being arranged on the side of the first outputterminal; and a cascade circuit, which provides a voltage for startingthe high-pressure discharge lamp at the output of said circuit, theoutput of the cascade circuit being formed by the auxiliary electrodeand the second output terminal of the auxiliary starting circuit; and amatching network, which is coupled between the first and the secondinput terminal of the auxiliary starting circuit and the first and thesecond terminal of the resonant capacitor, wherein the matching networkcomprises a first and a second inductance, the first inductance beingcoupled in series between the first input terminal of the auxiliarystarting circuit and the first terminal of the resonant capacitor, andthe second inductance being coupled in series between the second inputterminal of the auxiliary starting circuit and the second terminal ofthe resonant capacitor, wherein the method comprises: a) generating avoltage for starting the high-pressure discharge lamp by a cascadecircuit, which is comprised by the auxiliary starting circuit; and b)providing the voltage for starting the high-pressure discharge lampbetween the auxiliary electrode and the second output terminal of theauxiliary starting circuit.